16 CFR 23.1 - Deception (general).
It is unfair or deceptive to misrepresent the type, kind, grade, quality, quantity, metallic content, size, weight, cut, color, character, treatment, substance, durability, serviceability, origin, price, value, preparation, production, manufacture, distribution, or any other material aspect of an industry product.
If, in the sale or offering for sale of an industry product, any representation is made as to the grade assigned the product, the identity of the grading system used should be disclosed.
To prevent deception, any qualifications or disclosures, such as those described in the guides, should be sufficiently clear and prominent. Clarity of language, relative type size and proximity to the claim being qualified, and an absence of contrary claims that could undercut effectiveness, will maximize the likelihood that the qualifications and disclosures are appropriately clear and prominent.
An illustration or depiction of a diamond or other gemstone that portrays it in greater than its actual size may mislead consumers, unless a disclosure is made about the item's true size.